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IMPALA keeps cracking plug

Hey Everyone!

My father has a 2000 Chevy IMPALA, he is trying to decide whether to keep or sell. The car has 176, 600 miles on it. The problem is that the car keeps cracking the spark plug ( the 3rd spark plug) This is a six cylinder car. We have had new ignition coil, sensors, plug wires, security sensors put on this car. Our mechanic of 30 plus years, does not know what is the cause of this problem.

When driving this car it runs fine. However, when stopped or going slow the engine stalls. However, it always(knock on wood) starts right back up. Any help or advice would be appreciated. We have till the end of March due to the fact the car will not pass VA safety inspect, unless we can locate and fix the problem.


Will it not pass inspection because of a Check engine light on? If that is the only thing causing the CEL I would just replace the plug get it inspected. How often has the “cracked plug” (BTW "the 3rd spark plug"doesn’t tell us anything) happened?

What part of the plug cracks? Outside or inside?
If it’s the center ceramic inside detonation is a possibility.
Does it ping on acceleration?
Check the EGR passages in the intake manifold, if it has them.
The passage to #3 could be clogged.
Does your father do a lot of short trips and gentle acceleration?
That can promote carbon buildup.

Make sure the right plugs were put in! If not oem change them out and go from there.

Here’s some food for thought . . .

There is a vehicle in our fleet that kept cracking and fouling the same plug, every few months

I did some digging, and found a torn intake gasket . . . located at the cylinder with the “bad” plugs

Once I replaced the intake gasket and the plug once again, it’s never come back for the same problem again

The plug cracks about every 200 miles. My understanding is that the plug is cracked inside.

My father does mostly does a cross between city and interstate driving. Since this problem has started, he has been afraid to take it on the interstate. He is easy on gas and pedal.

The’s windshied got a crack in the wind shield from a rock hitting it. A new wind shield, is needed before the car will/can pass safety. However, we do not want to install a new window if we can not fix the running issue.

Thanks for advice folks!!

I think @db4690’s note about the intake gasket is worth noting - since the engines in that car are well known for intake manifold gasket issues.

I had a problem on a 1990 Ford Aerostar with the ceramic tip around the center electrode of the spark plug cracking. It turned out that coolant was leaking into the cylinder and causing the inside of the plug to crack. In my case, it was a crack in the cylinder head. Fortunately, the Aerostar was still on warranty.

A vacuum leak can also be the reason the engine is stalling at idle. A vacuum leak can also be covered up at highway speeds so that is why you may not notice it on the road.

The mechanic could throw a vacuum gauge on the engine, assuming he has one, and any vacuum issue should be seen instantly on the gauge.

Every 200 miles? Sheesh. I would look for a lean detonation problem with that cylinder. Many of the potential causes have already been listed…

Just curious, is the ground electrode on the plugs you’re using a traditional tang and if so, is it deformed in any way or does it look normal?

A lean cylinder was the first thing that came to my mind too. A vacuum leak is an excellent suspect. A partially clogged injector is another. Injectors can be bench tested, or readily changed. It’s worth a try.

We have checked thoroughly for vacuum leaks and our mechanic has also, checked for vacuum leaks and stopped up injectors. However, we have not checked for a cracked cylinder head or damaged manifold gaskets.

The plugs that are installed in the IMPLA are standard middle of the road plugs, bought from NAPA.

Thanks everyone for advice thus far. As soon, as I know something, else, I will let ya’ll know.

Had a Buick 3800 a few years back that would crack the number one plug on test drive after replacement. Found no lean issues with that cylinder. Replaced platinum plug with an iridium plug and it never cracked again.

If I had this problem and vacuum leaks has been eliminated and there were no DTC’s I’d do a compression and cylinder leak down test next.

Was the injector bench tested for volume and spray pattern? A partially clogged injector will still spray, but leaves the cylinder too lean. That’s like using a bellows in a fireplace, it causes intense heat. Intense heat is the usual cause of fractured plugs. It can also cause a single cylinder to preignite from the combined high residual heat and heat from compression, and that’ll crack a plug.

It might not ultimately turn out to be the injector, I just wanted to clarify my suggestion.

Good analogy TSM comparing a bellows blowing extra air into a fireplace and the resulting extreme temperatures to a lean burn condition in an engine cylinder.

Thanks. Hopefully the OP will consider the question and post back with an answer.

Just some food for thought, but an EGR issue is always a possibility. The car apparently sees a lot of road use based on age and miles. That means a lot of EGR operation.

In theory anyway, an EGR issue should affect all cylinders but due to airflow in the intake and the computerized timing controls it’s at least possible for one cylinder to be more affected than others.

Having torn down a number of damaged engines due to pinging, I have noticed that in every case one cylinder was affected more than others.
One piston is wiped out, the next in line damaged but not as bad, the third mildly damaged, and the 4th with no noticeable damage at all. (Of course that’s using a 4 cylinder as an example.)

The same theory could carry over to spark plug damage and thankfully it’s plugs instead of pistons. Maybe a borescope looksee into the suspect cylinder for an examination of the piston top and valve heads would be in order.

On ok4450’s thoughts, Escort and Focus 1.9L and 2.0L engines are known to drop valve seats. The most common one to go is #4 - on the back of the engine nearest where the EGR feeds. I’ve seen the “theory” that these engines that lack EGR valves (I think those in Canada?) are not so likely to lose their valve seats. Of course, since this is a problem that Ford has never even glanced at there are no “data” to go with that theory.

EGR systems can also be pretty far out of whack before setting codes.

So, the short story is that I think checking out the EGR system is worth a look.

I agree.

For the OP’s information, the EGR (Exhaust Gas Recirculation) system’s function is to prevent excess combustion heat in the cylinders by allowing a tiny bit of inert exhaust gas to displace a bit of the air being drawn into the engine. The slight reduction in free oxygen reduces the combustion temps, like closing the vent a bit on a woodstove to reduce the heat. The oxygen in the exhaust gasses are already bound up with carbon and sometimes nitrogen, so they cannot contribute to combustion.